In today's workplace, people frequently create resources on which other people perform various activities. For example, one person could create a web page and another person could download the web page, print the web page, copy information out of the web page, or perform other types of activity with regard to the web page. In another example, one person could send an email message to another user. In this example, the other user can then read the email message, reply to the email message, forward the email message, or perform some other type of activity with regard to the email message.
In many circumstances, it would be helpful to know what activities people performed with regard to resources and who performed the activities. For example, a user sends out an important email message to a group of colleagues. In this example, it would be helpful for the user to know which of the user's colleagues have read the email message. In another example, a person has asked his supervisor to review a document. In this example, it would be helpful for the user to know whether the supervisor has looked at the document yet.